Recently, a differential signal is transmitted through a transmission path so that communication is performed. The transmission path includes a pair of signal wires. In this case, it is necessary to remove a common mode noise, which is applied in each signal wire. Here, the common mode noise is defined on the basis of a ground level. For example, in JP-A-2005-244351, a choke coil for blocking a differential signal in a normal mode and for passing a common mode noise is connected between the transmission path and a ground.
However, in the above case, since the choke coil is always connected between the transmission path and the ground, a capacitance between the pair of signal wires increases, so that a communication signal may be affected by the capacitance. Thus, it is requested to remove the common mode noise without affecting a waveform of the communication signal.